A ship carrying 200 tonnes of ammonium nitrate sank offshore Costa Rican town of Puntarenas.
The incident forced the government to establish an emergency zone along 100 km of the coast and to ban fishing and swimming.
The toxic chemicals that the ship was carrying are used in production on fertilizers and explosives.
Government officials said an enquiry into who was responsible for the ship sinking and the spillage would begin as soon as possible, BBC reported.
According to other media reports, the ship was transporting the chemical to fertilizer firm Fertilizantes de Centroamerica.
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